Merrill Lynch’s plan to potentially ease off its pledge to completely do away with commission-based retirement accounts may not provide relief to retirement clients who want to keep using Wall Street’s traditional sales model.

The Bank of America Corp.-owned unit told brokers Thursday that it is considering alternatives for clients in “limited situations” where individual retirement accounts that charge a fee based on a percentage of assets wouldn’t be in their best interest, according to a memo from Merrill head Andy Sieg...